To make informed decisions, assessment theorists, researchers, and practitioners can evaluate the overlap among (1) relevant theories, (2) empirical contributions, and (3) best practices. Unfortunately, such a task may seem daunting due to the so-called science-practice gap, which can thwart collaboration among these parties. This paper presents an epistemology for delineating the importance of integrating these three sources of knowledge. We then apply this epistemology to show that our current knowledge of assessment and development topics are well integrated in some places, but still quite lacking in others.